DoFn is not a functional interface, so lambdas won't work with it. If you look at MapElements and FlatMapElements, these are transforms built on top of ParDo that allow passing a lambda. Unfortunately, due to issues with type erasure and Java generics, when using a lambda it is necessary to specify the output types as well. You can see an example of this in the java8tests:
https://github.com/apache/incubator-beam/blob/master/sdks/java/java8tests/src/test/java/org/apache/beam/sdk/transforms/MapElementsJava8Test.java#L49 Unfortunately, this still won't work well for your use case since the lambda doesn't have access to the timestamp. On Tue, May 17, 2016 at 5:41 PM Jesse Anderson <[email protected]> wrote: > Is there a way to create a DoFN with a lambda function? The DoFN class > itself should support it, but the overloading of the ParDo.of causes > ambiguity for a lambda function. Is there a different way to accomplish > this? > > To answer the why would you want this: > > static class EnrichWithTimestampFN extends DoFn<KV<String, Long>, > KV<String, KV<Instant, Long>>> { > @Override > public void processElement(DoFn<KV<String, Long>, KV<String, > KV<Instant, Long>>>.ProcessContext context) throws Exception { > context.output(KV.of(context.element().getKey(), > KV.of(context.timestamp(), context.element().getValue()))); > } > } > > This is a DoFN that I wrote to enrich a PCollection with a the time > (Instant). I need the access to the ProcessContext to get the timestamp. > This would be much easier expressed with a lambda. > > Thanks, > > Jesse >
